This invention relates to an in-process nondestructive testing method utilizing an ultrasonic wave to test welds formed by resistance welding techniques, and to an apparatus for carrying out the same.
Heretofore, the nondestructive testing of spot welded portions through the use of an ultrasonic reflectoscope has been commonly effected in a testing step carried out separately from the welding steps carried out for forming spot welded portions. When using the ultrasonic reflectoscope, the probe thereof has been placed on the welded portion to be tested, and the state of the weld has been determined by the observation of a corresponding waveform produced by multiple reflections and displayed on a Braun tube connected thereto. This has resulted in the disadvantages that the test consumes a relatively lone period of time and the interpretation may be different for different inspectors because the test is not quantitative.
Also among conventional methods of effecting nondestructive test of welded members by the use of an ultrasonic wave and in an in-process manner or during the welding operation, there is known what is called a transmission method. According to this transmission method, a transmitting ultrasonic vibrator is secured to one of a pair of electrodes having sandwiched therebetween members being welded and a receiving ultrasonic vibrator is secured to the other electrode, so that an ultrasonic wave from the transmitting vibrator is transmitted to the receiving vibrator through the members undergoing welding. Then a Braun tube is used to observe any change in the amount of transmission of the ultrasonic wave. The transmission method has brought about a great reduction in testing time and a large increase in testing reliability but it has been disadvantageous because of the necessity of using both transmitting and receiving vibrators.
Further vibrator reflection methods are known which use transmitting and receiving ultrasonic vibrator mounted on one of a pair of electrodes having sandwiched therebetween members being welded to effect a nondestructive test by the utilization of the phenomenon of reflection. These reflection methods are disadvantageous in that the condition of the weld is determined with a very low accuracy because of the utilization of the ultrasonic wave reflected from either the end of surface of that electrode having the vibrator secured thereto or from an interface between such an electrode and the adjacent member being welded.
It is an object of the present invention to provide a new and improved nondestructive testing method for determining the condition of the weld between of members being welded with a high accuracy during the welding operation by using a single ultrasonic vibrator serving as both a transmitter and a receiver.
It is another object of the present invention to provide an apparatus for carrying out the testing method as described in the preceding paragraph which has a simple construction.